Nittala 5 Sarma
School of Chemistry
Chemistry Concepts and Vocabulary from Root Words
Andhra University,
Visakhapatnam 530 003, India
Email: [email protected]
Although chemistry impacts largely on the society and
civilization, the subject is still viewed with awe. This is
because the language of chemistry of which the technical
terms are an integral component, is not easily comprehensible
even for the practicing scientists; let alone the layman.
However, many of these terms, in English, can be noted as
derived from a few affixes of Greek and Latin origin, e.g.,
ortho, tropo, mer, meta, iso, para, hetero, syn, homo, tapo, dia
andpseudo. Identifying the roots from which a term is formed
can help understand it better, and even predict what a new
term to be encountered stands for. The meanings and
significance of various root words occurring in technical terms
as also several unique words of chemistry are explained.
1. Introduction
The word alchemy is Arabic
but its actual source is traced
to more than one, e.g., Khem
(Egypt! or Khemia (Greek word
for melting and alloying of metals!.
- Editor's note
Keywords
Introductory chemistry, interdisciplinary, vocabulary, language
of chemistry, curriculum.
Alchemy (Arabic: al the; chymia fluid)l was the Egyptian art of
'pouring' to convert other metals into gold and in the preparation
of the elixir oflife. Xenobiotics (Greek: xenos guest/stranger; bios
life) are man-made chemicals foreign to the Earth's ecosystem.
From alchemy to the xenobiotics, the journey of chemistry was
an intimate involvement with the progress of civilization. Several
common terms of the day got into chemical vocabulary and in
course of time, the vice versa also happened, enriching the
language. Over the years, chemists have enjoyed exclusivitysocial as well as scientific. This is not only a tribute to them for
their achievements, but also a reminder of their inaccessibility
and tendency to treat good chemistry as their preserve. In the
present chemical age, more than ever before, chemistry needs to
be taken to the masses, and particularly to the non-specialists,
including but not limited to the specialists of other branches
working on the borders of chemistry. This can probably be
promoted by explaining the language of chemistry in more
simple terms. Chemistry language consists of (i) symbols,
formulae and chemical equations, on which several reviews/
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monographs are available, and (ii) vocabulary of chemical terms,
on which the available information is extremely limited.
Dictionaries [1,2] or glossaries [3] and standard textbooks of
chemistry [4-7] do serve as reference material, but do not provide
a systematic vocabulary learning vis a vis the concepts. In fact, it
is the common experience that many terms might be understood
per se but that their origins are not known so well. This acts as a
limiting factor as one advances. For in all phenomena, including
the learning process, the law of diminishing returns applies
restricting the continued ability of the learner. On the other
hand, acquiring new knowledge can become a child's play if the
structure and the organization of the chemical terms are known
well.
As classical Greek
and Latin languages
are not spoken now
having been replaced
by modern Greek and
Italian, the meanings
of the classical Latin
and Greek roots have
not changed, unlike
what could have
happened if the
languages were in
common use.
The word English itselfis from 'Angleish', the Germanic language
of the immigrant Anglo Saxons (AD 450-550) of the British Isles.
Hence, it is no wonder that upon the Norman conquest (AD
1066) of England, and the consequent influence of scientific
scholars and their scholarly languages of Latin and Greek that
followed, classical Greek and Latin terms were adopted for the
new scientific concepts that developed. As these classical
languages are not spoken now having been replaced by modern
Greek and Italian, the meanings of the classical Latin and Greek
roots have not changed, unlike what could have happened if the
languages were in common use. Hence, from the language point
of view, the terms have a sort of permanence. But from the
(dynamic) science point of view, the terms can at best indicate
the level of knowledge that existed. For, as the concepts get more
and more refined due to advancement of science, the terms
coined originally may not fully explain, nay mislead occasionally.
In such a situation, stretching the etymology approach beyond a
point may prove counter-productive. The IUPAC have done
yeomen service by standardizing the chemistry terms, defining
them precisely and in quite a few cases, recommending the use of
new terms in place of old confusing ones [3]. However, in the
case of most chemistry terms in use, the etymology approach can
be extremely useful to a new starter, and perhaps educators.
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The origin of each
term, and in a few
cases their historical
background were
probed from
available literature.
2. Methodology
An extensive list of technical terms in current popular usage was
initially prepared from the IUPAC Compendium [3] and standard
textbooks of various branches of chemistry [4-7]. From this list,
such terms involving not-so-obvious etymology were sifted out.
The origin of each term, and in a few cases their historical
background were probed from available literature. [3-7] The
chemistry terms for which the information is thus available in a
piecemeal fashion, were then grouped under substantive topics
with minimum possible overlap. The inclusion of a term in a
particular topic and sequence was based on continuity of the
cumulative account and its effectiveness in terms of clarity,
objectivity and freedom from redundancy. Due to the space
constraint, illustrations of chemical structures are avoided, even
though it could have added to the clarity of the terms (concepts)
being described. The abbreviations Gr., L., and Ger. stand
respectively for Greek, Latin and German throughout.
3. Approach
In a stand alone article, I have recently presented a few foreign
(Greek, Latin, French and German) roots from which many
organic chemistry terms are formed [8]. In the present article, I
concentrate on the generic origin and significance of various
general chemistry terms from the domains of physical chemistry
and inorganic chemistry.
Let us examine the
Greek root kata (or
cata). It has
different related
meanings: down/
back/in order.
As an illustration of the approach, let us examine the Greek root
kata (or cata). It has different related meanings: down/back/in
order. Catalyst (Zein to loosen), cataphoresis (phorein to bear),
catabolism and katamorphism are words in the first sense. A
catalyst helps break bond(s). In cataphoresis (which is the same
as electrophoresis), migration (of the charge-bearing suspended
particles, e.g., protein macromolecules) takes place under the
influence of an electric field. Catabolism is the breakdown of
complex organic molecules by living organisms (resulting in the
liberation of energy). Katamorphism (morphe shape), in the field
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of geology, is the breaking-down process of metamorphism, as
opposed to the building up process of anamorphism (ana up). In
the sense of 'back', catalkata is present in catacoustics/cataphonics
- the branch of acoustics that deals with echoes. In the third
sense of 'in order', the catalogues (legein to reckon) of books,
chemicals etc. are well known.
In triboluminescence
(Gr. tribein to rub),
light results from the
rubbing together of
the surface of certain
solids.
The now common word 'atom' (Gr. a without, tomos to slice)
coined by Dalton, means unsliceable. The knowledge of the
etymology of 'atom' is helpful to comprehend terms like tomography, microtome, hysterectomy, etc [8]. The term 'molecule' is
from moles that means mass in Latin.
4. Discussion
4.1 Lighting Up
'Lumen' is light in Latin. 'Luminescence' is emission of light
otherwise than by incandescence (and so at a relatively cool
temperature); its mechanism is chemical in chemiluminescence
and biochemical in bioluminescence (Gr. bios life). In
triboluminescence (Gr. tribein to rub), light results from the
rubbing together of the surface of certain solids. 'Piezoluminescence' (Gr. piezein to press; piezochemistry is the study of
the effect of high pressures on chemical reactions; piezoelectricity
is the electric polarization of some anisotropic stress-deformed
crystals) is the luminescence observed when certain solids are
subjected to a change in pressure. Sonoluminescence (L. sonare
to sound) is induced by sound waves.
The suffix 'escence' of these terms, of Latin origin, indicates an
inchoative meaning, [1] and is present in terms e.g., iridescence,
opalescence, fluorescence, effervescence, etc. In iridescence (Gr.
iris rainbow), a play of colours is caused by interference as on
bubbles. Opalescence is milky iridescence. Fluorescence of
substances such as fluor (spar) is the emission of light of larger
wavelength than that to which the substance is exposed. On
removal of the source, the fluorescence disappears. But in phosphorescence of substances such as phosphor, the luminescence
The suffix 'escence'
of these terms, of
Latin origin, indicates
an inchoative
meaning, [1] and is
present in terms e.g.,
iridescence,
opalescence,
fluorescence,
effervescence, etc.
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The solutions exert
pressure, called
osmotic pressure
(Gr.osmos
impulse, to push).
persists for more than 0.1 nano seconds after excitation. The
action of acid on carbonates causes effervescence (L. fervere to
boil) of carbon dioxide.
4.2 Principle Bound
Colligative (Gr. col together; ligare to bind) properties are the
properties coming under a general principle. In a solution, these
properties are dependent on the concentration of solute, and not
on its nature. The solutions exert pressure, called osmotic
pressure (Gr. osmos impulse, to push). (As a side note, osme, in
Greek means odour, a reason why the element osmium was called
so). The osmotic pressure depends on the tone differential (Gr.
tonos pitch, tension; L. tonus) of two solutions across a semipermeable membrane. Osmolality and osmolarity (now replaced
with osmotic concentration) are quantitative expressions based
on the rational activity of water [3].
Cryoscopy (Gr. cryos frost) is the study of the effect of dissolved
substances on the freezing points of solvents. Ebullioscopy (L. e
out; bullier to boil) is the study of the effect of dissolved substances
on the boiling point of solvents.
4.3 Bound in Deed
A ligand (Gr. ligare to
bind) is an atom/
molecule/radical/ion,
which forms a complex
with a central atom.
The suffix and (that
signifies the specific
purpose) of ligand is
present in coronand,
cavitand, cryptand,
podand,spherand,etc.
A ligand (Gr. ligare to bind; see above) is an atom/molecule/
radical/ion, which forms a complex with a central atom. The
suffix and (that signifies the specific purpose) ofligand is present
in coronand, cavitand, cryptand, podand, spherand, etc. They
rhyme with errand (Old Norrish arr messenger). A coronand (L.
coranus crown) is a monocyclic ligand assembly that contains
three or more binding sites, e.g., the 0 atoms of crown ether; the
resulting adduct is called coronate. Cavitands are compounds
having a cavity large enough to host/accommodate other
molecules. The products are inclusion compounds. A cryptand
(Gr. kryptos hidden) like a coronand, is also a molecule with three
or more binding sites held together by covalent bonds, and
having a cavity; but in which another molecular entity can hide
by bonding with the binding sites. The terms podand and
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spherand are used for certain specific ligand assemblies [4].
In mathematics, similar rhyming terms are operand, multiplicand,
radicand, summand, etc. An operand is a quantity upon which a
mathematical operation is performed. A multiplicand is a number
to be multiplied by another. A radicand is the quantity under a
radical sign. A summand is a part of a sum. In psychology,
analysand is a person undergoing psychoanalysis.
Catena, in Latin,
means chain.
Catenation (of
carbon) is involved in
most organic and
some inorganic
compounds.
Hapticity (Gr. haptein to fasten) is the number of ligand atoms
simultaneously bound to a metal cluster. Chela is the latinised
form of chele in Greek. It is the prehensile claw of an arthropod
(animal). Chelate is a coordination compound in which a central
metallic ion is attached to an organic molecule at two or more
positions. In Latin, clathrare is to furnish with a lattice. Clathrate
is a molecular compound having one component enclosed in the
cavities of another component. Clathrochelates have both the
features of chelate and clathrate, e.g., the cage complex formed
from dimethylglyoxime, BF 3 and Co (III). They are also called
cryptates, since the metal (Co) is hidden at the center of the cage.
Agostos in Greek is to clasp/to draw towards/to hold oneself.
Agostic designates structures in which a H atom is bonded to a C
(or Si) atom as well as (an unsaturated) metal centre.
Catena, in Latin, means chain. Catenation (of carbon) is involved
in most organic and some inorganic compounds. In naming the
inorganic and co-ordination polymers, as per the IUP AC
nomenclature, the constitutional repeating unit (CRU) is first
selected and suitably prefixed. For example, the polymer
[Sn(CH 3)2]n is named as catena-poly[dimethyl tin] [9].
4.4 Kinds of Sorption
Sorption (L. sorbere to suck in) is of different types - absorption
(ab from), adsorption (ad to), physisorption, chemisorption and
perisorption. The ab/ad duo is illustrated with the Latin phrases
ab initio (from the beginning, i.e., from scratch) models, and ad
infinitum (to limitless end, i.e., infinite) dilution. In absorption,
the whole of the absorbing medium (solid or liquid) is engaged,
Sorption (L. sorbere
to suck in) is of
different types absorption (ab from),
adsorption (ad to) ,
physisorption,
chemisorption and
peri sorption .
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The prefix 'syn' (Gr.
syn together) is
associated with
synchronous (chronos
time), synopsis/
synoptic (opsis view),
synthesis (thesis a
placing; if the placing
is only an assumption
that is yet to be
tested, it becomes
hypothesis), etc.
e.g., (photometric) absorption coefficient. In adsorption, the
surface layer only is involved, e.g., adsorption chromatography,
adsorption hysteresis, adsorption isostere, adsorption isotherm,
and adsorption potential. In hysteresis, the effect lags behind its
cause; adsorption hysteresis (Gr. hysteros later) occurs when
adsorption and desorption values deviate from one another.
Stereos is solid in Greek. Adsorption isostere (Gr. isos equal) is for
a given (the same) amount of solid - its capacity of adsorbing a
constant (or costant excess) amount of substance under different
pressure-temperature conditions.
Physisorption is the abbreviation of physical adsorption, and
chemisorption of chemical adsorption. Perisorption (Gr. peri
thorough) is an extremely effective adsorption of a gas by a solid
with the formation of an almost molecular mixture of the two
substances.
4.5 Placing Together
The prefix 'syn' (Gr.syn together) is associated with synchronous
(chronos time), synopsis/synoptic (opsis view), synthesis (thesis a
placing; if the placing is only an assumption that is yet to be
tested,. it becomes hypothesis; biosynthesis and photosynthesis
are mediated through the action of bios and photos, i.e., life and
light respectively), etc. Sym is an identical prefix, as in symbiosis
and symposium (posis drinking). Perhaps, the symposia were
meant to celebrate the scientific successes than for deliberations!
4.6 Good to be
'Eu' is a Greek prefix, meaning good. 'Eutectic' (Gr. tekein to
melt) relates to a mixture of two or more substances having a
minimum melting point. Such a mixture behaves in some
respects like a pure compound. Because of the sharp melting
point, the eutectic mixture was originally thought to be a single
compound. A eutectic mixture, in aqueous solution, is called
cryohydrate, and the eutectic point as the cryohydric point (see
above for cryo). The property of being easily melted is called
'eutexia'. A eucolloid (Gr. kolla glue, eidos form) has a large
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particle diameter, more than 250 nm. In a euatmotic reaction, a
single vapour phase is produced during an isothermal, reversible
reaction between two (or more) solid phases. A euhedral (hedra
base) crystal has well defined faces (it is also called an idiom orphic
crystal; idios own, distinct in Greek), formed due to the free room
available during crystallisation. Its opposite is allotriomorphic
(see before) crystal.
'/505' in Greek is
for equal. With iso
as prefix, several
terms occur.
4.7 Equal in Some Way
'/sos' in Greek is for equal (see above). With iso as prefix, several
terms occur, e.g., isobar (Gr. baros weight), isoelectric point,
isohydric solutions, isenthalpic reactions, isomerism (meros part),
isomorphism (morphe shape), isopleth (plethos great number),
isotactic/isotaxy (taxis arrangement), isothermal (therme heat;
read temperature!), isotonic (tonos pitch), isotope (topos place)
and so on.
In atmospheric chemistry, charts are prepared ofproperty isolines.
Isochore (Gr. chora space) is a curve relating quantities measured
under conditions in which the volume remains constant.
Isohaline (Gr. halos salt) is a line drawn on a map through points
of equal salinity in the sea. Isohyet (Gr. hyetos rain) is a contour
line of equal rainfall. Isopiestic (Gr. piezein to press) is of a
system (with conditions described) having equal pressure
throughout. Isopycnic (or isopycnal) (Gr. pyknos dense) is a line
on a chart joining points of the same atmospheric (or ocean
water) density. Isotach (Gr. tachys swift) is a line on a chart
joining points of equal wind speed.
Isotopomer (Gr.
4.8 Similar and Different
4.8.1 Similar (Iso/homo): Isotopes (topos place) occupy the same
place (position) in the periodic table; that of the same element.
Isobars (baros heavy) have the same number of the mass
contributing neutrons and protons together. Isotones are nuclei
of different elements but with the same number of neutrons.
Isodiapheres (Gr. pherein to carry) are nuclides having the same
difference between totals of neutrons and protons. Isologues are
mer05 part) is the
contraction of
isotopic isomer.
Isotopomers have
the same number of
each isotopic atom
but differing in their
positions.
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Isozyme, or
isoenzyme is one of
a group of related
enzymes catalysing
the same reaction
but having different
chemical, physical,
and biochemical
properties.
compounds with similar molecular structure but containing
different atoms of the same valency. Isotopomer (Gr. meros part)
is the contraction of isotopic isomer. Isotopomers have the same
number of each isotopic atom but differing in their positions.
Isotopomers can be either constitutional isomers or isotopic
stereoisomers. The suffix mer occurs in various other terms, e.g.,
elastomer (Gr. elastikos to drive), rotamer, etc. This affix, in coordination nomenclature, means meridional (mer-isomer), as
opposed to facial (fae-isomer), two geometrical descriptors, apart
from eis and trans. Isotopologue is a molecular entity that differs
only in isotopic composition, e.g., HzO, HOD, DzO. Isozyme, or
isoenzyme is one of a group of related enzymes catalysing the
same reaction but having different chemical, physical, and
biochemical properties.
Isohydric solutions have the same H+ ion concentration (pH
value). Isoelectric point is the pH at which conductivity (and
viscosity) is minimum. An isodisperse substance is dispersible
in solutions having the same pH. Isovalent resonance is the form
of resonance in which all resonance structures contain the same
number of bonds. Isosteric (Gr. stereos solid) molecules have
similar size and shape.
In crystallography, isometric system is the cubic system.
Isodimorphous substances exist in two isomorphous crystalline
forms. Isodesmic structure (Gr. desmos a chain; desme bundle) is
crystal structure with equal lattice bonding in all directions (and
no distinct internal groups).
Isohydric solutions
have the same H+
ion concentration
(pH value).
Isoelectric point is
the pH at which
conductivity (and
viscosity) is
minimum.
Isocycles have the same element in the nng structure.
Isopolyanions are polymeric anions in which no extra elements
are present. Isopoly anions are very stable complexes, e.g.,
heptamolydate, also called as the paramolybdate ((M0 70 Z4 )fr-).
A prefix of similar meaning is homo (Gr. homos similar), e.g.,
homocycles, homovalent resonance, homopolar bond, etc. The
homopolar bond is more commonly known as covalent bond. A
homoazeotrope (Gr. zeiin to boil; see zeolites below) has only one
liquid phase distilling without change of composition.
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Homopolymers contain a single monomer as the repeating unit,
e.g., polythene (ethylene is the monomer) and natural rubber
(isoprene is the monomer). Homochiral is when the optical
isomers are enantiomerically (in old literature, enantiomers were
referred to as antipodes) pure (enantiopure). Complexes with
only one type ofligand are called homoleptic (Gr.leptos slender).
Superposable ligands are called homomorphic. Homotopic
groups (or atoms) of a molecule are those related by an n-fold
(n=2,3, etc.) rotation axis, e.g., CI atom in CHCl 3 (3-fold) and
COOH group in chiral tartaric acid (2-fold).
The opposite of
iso/homo is hetero
(Gr. heteros other),
e.g., heterocycles,
heterovalent
resonance, etc.
4.8.2 Different (Hetero): The opposite of iso/homo is hetero (Gr.
heteros other), e.g., heterocycles, heterovalent resonance, etc.
Heterovalent resonance is when the various resonance structures
contain different number of bonds. Heteropolar bond is an ionic
bond and is known by other names also, e.g., electrovalent bond,
polar bond, and electrostatic bond. A heteroazeotrope has two or
more liquid phases distilli~g without change of mean
composition. The opposite of this is heterozeotrope with liquid
constituents of limited miscibility. Heteropolymers contain
monomers of different structures and heteroleptic complexes
have different ligands.
Homocatenation is when only one element/structural moiety is
involved, and heterocatenation is when different elements (as in
pyrophosphate) are involved. Heteropoly anions, with appropriate elements embedded in the cage structure e.g., (PMo 1Z 0 40 )3are more stable than isopolyanions.
4.9 Negation
'A' (or 'an') is a prefix
used for opposite
meanings, e.g.,
amorphous (morphe
shape), anharmonic
'A' (or 'an') is a prefix used for opposite meanings, e.g., amorphous
(morphe shape), anharmonic (Gr. harmos a joint fitting), asymptotic
(Gr. a + sym together+ ptotos apt to fall), aneroid (Gr. neros
wet+eidos form), etc. Agranular carbon is a monogranular or
monolithic carbon material with homogeneous microstructure.
Aglycon (or, aglycone) is the non-sugar compound remaining
after replacement of the glycosyl group from a glycoside by a
(Gr. harmos a joint
fitting), asymptotic
(Gr. a+ sym
together + ptotos apt
to fall), aneroid (Gr.
neros wet+eidos
form), etc.
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II, im and in are
similar-meaning
prefixes, often in the
negative sense like
un, e.g., imbalance,
immiscible,
impermeable,
inactive, incongruent.
But in quite a few
cases, they are also
used in the positive
sense.
H atom. Agonist, in English means attack/threat. In
(bio )chemistry, it stands for a substance that can bind to cell
receptors and produce its own response. The opposite of agonist
is antagonist. Antagonist is a substance that reverses or reduces
the effect induced by an agonist.
4.10 Antagonism - But not Always
De (L. off/from) is usually a prefix used when an opposite
meaning is to be conveyed, e.g., decoupling, degenerate ( = fallen
from a noble state; degenerate orbitals have about the same
energy), dehydration, denatured (spirit), demulsification,
descending (order) etc. However, in desiccation (L. sicca dry)
and deliquescent (L. scendo growing! becoming), de is used as an
affirmative prefix.
11, im and in are similar-meaning prefixes, often in the negative
sense like un, e.g., imbalance, immiscible, impermeable, inactive,
incongruent (L. conguere to run together, e.g., incongruent
melting), indistinguishable, indivisible, inelastic, inert, insignificant etc. But in quite a few cases, they are also used in the
positive sense, e.g., illuminate, illustrate, implant, incandescent
(L. candere to glow), incinerate (L. cineris ashes), incline (L.
clinare to lean), inflammable, innoculate, inseminate, insect (L.
secare to cut), etc.
4.11 False (Pseudo)
Pseudo means false in Greek. This prefix pseudo also occurs in a
variety of other contexts, e.g., pseudoaxial, pseudoequatorial,
pseudo (zero, first, second, etc.) order reactions, pseudopericyc1ic
(transformation), pseudo-copolymer, pseudooligomer, pseudoreversible (indicator), and pseudoureas (isoureas; now
obsolescent).
In cyc10pentane ring, puckering occurs due to the strain which,
however, rotates among the 5 carbons in such a way that at any
given time, no particular Cis out-of-plane. This effect is called
pseudorotation. A special case of pseudorotation is Berry pseudo
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rotation. In the trigonal bipyramid (TBP) molecule like that of
PF5' two F atoms should behave differently from the 3 others.
However, they behave identically (as shown in the 19F NMR) due
to a fast scrambling resulting in a new TBP structure (via a
square planar transition state). Because the two TBP structures
are related to each other by simple rotation, the process is called
pseudorotation. As this was first suggested by Berry, it is also
called Berry pseudorotation.
4.12 Turning Related
Tropos, in Greek means 'a turn'. This root word is one of the
largest contributors of scientific terms, particularly of chemistry
and biology. Allotropy (allos different) is the existence of an
element in two or more solid, liquid or gaseous forms, in one
phase of matter. Allotropy owes its origin to differing bond
angles. For example in white phosphorus, P-P-P bond angle is
60° (tetrahedral) while in black phosphorus, the angle is 90-100°.
Polytropic processes are those that satisfy the condition PV =C,
where C is a constant. Isotropic (opposite: aniosotropic) medium
is one for which the physical properties e.g., magnetic susceptibility or elastic constants do not vary with direction. Thixotropy
(Gr. thixis action of touching) is the property of showing a temporary reduction in viscosity when shaken or stirred, e.g., paints.
Liquid crystals exhibiting thermotropy or lyotropy, do so when
the transition to liquid crystalline phase occurs as the temperature is changed, or as the composition of the liquid is changed
respectively. More terms based on tropos are included in Sections
4.13.1 and 4.15.
4.13 Off a normal phenomenon (Ortho, Para, Meta and Dia as
prefIXes)
In the trigonal
bipyramid (TBP)
molecule like that of
PF 5' two F atoms
should behave
differently from the 3
others. However,
they behave
identically (as shown
in the
19F
NMR) due
to a fast scrambling
resulting in a new
TBP structure (via a
square planar
transition state).
Tropos, in Greek
means 'a turn'
This root word is
one of the largest
contributors of
In Greek, orthos means straight, upright and correct,para means
beside, meta means after or beyond, and dia through. They are
used as prefixes for terms denoting the extent to which the true
phenomenon is away. Ortho denotes the most common form,
scientific terms,
particularly of
chemistry and
biology.
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The acids formed by
incomplete hydration
are called
meta
acids, e.g.,
metaphosphoric acid
(HP0 3 ), as opposed
to orthophosphoric
acid (H 3 P0 4).
com pared to Para and meta. The significance of these prefixes in
organic (aromatic) nomenclature is given in the precursor
paper [8].
4.13.1 Ortho: Orthohydrogen molecule is the right (or more
abundant) form; it has the more stable parallel spin combination
(triplet state) of the two H nuclei constituting it. When hydration
(of oxyacids to form acids) is complete, the corresponding acid is
called orthoacid., e.g., orthophosphoric acid H 3P04, by hydration
ofP Z05' Ortho is often implied; cf., arsenite (H zAs0 3-), bisulphite
(HS0 3-), borate (H zB0 3-), silicate (H 3SiO4-)' and vanadate
(H ZV0 4-), which are all orthoacid conjugates.
In orthogonal arrangement, right angles (90°) are involved. In
colloids, orthokinetic aggregation implies collisions (between
atomic/molecular entities) caused by hydrodynamic motions
(and perikinetic aggregation implies collisions caused by
Brownian motion).
4.13.2 Para: Para hydrogen molecule has the less stable antiparllel
spin combination (singlet state) of the two H nuclei; it constitutes
only ~ 25% at STP conditions, but an increasing fraction at low
temperatures. Paramagnetism is another (i.e., other than ferro)
magnetism, as in the 0z molecule. When placed between the
poles of a magnet, the molecules align themselves with the lines
of (magnetic) force.
Metastable phases
are thermodynamically unstable
phases (but they do
persist because the
transition is kinetically
hindered). Diamond
is a metastable
phase of carbon, the
stable phase being
graphite.
4.13.3 Meta: The acids formed by incomplete hydration are
called meta acids, e.g., metaphosphoric acid (HP0 3), as opposed
to orthophosphoric acid (H 3P0 4). The meta acids corresponding
to the above ortho acid conjugates (Section 4.13.1) are meta arsenite
(AsO z-)' meta bisulphite (also called pyrosulphite, S20/-), meta
borate (BO z-)' meta silicate (HSi0 3-), and meta vanadate (V0 3-).
The periodate (104-) is referred only as meta periodate.
The oxide of tungsten W0 3 is the parent of (ortho) tungstic acid
H 2W0 4, and isopoly acids (see above for iso), the conjugates of
which are meta tungstate (Hz W 1Z0 40 6-), para tungstate A
(W70 Z4 6-), andparatungstate B (HzW 1Z0 4Z 10-). Their designation
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follows the fact that for a uniform association of 3 molecules of
H 20, 3,9, 7, and 6 molecules ofW0 3 are required for the four
tungstates respectively.
Metastable phases are thermodynamically unstable phases (but
they do persist because the transition is kinetically hindered).
Diamond is a metastable phase of carbon, the stable phase being
graphite. Metatectoid (also called peritectoid; Gr. tekton craftsman
of a building/construction) reaction is a solid state (isothermal,
reversible) reaction of different phases producing a decreased
(by one at a time) number of new solid phases, like a mason does
to bricks while constructing a building.
Adiabatic (Gr. batos
passable) is when no
heat flow takes place
during a change in
state. As opposed to
adiabatic boundary,
the diathermic
boundary permits
energy transfer as
heat.
4.13.4 Dia: In diamagnetism, the molecules (mostly) allow the
magnetic lines of force through them without realigning
themselves (at the finer level however, they experience weak
repulsive forces and are realigned in the opposite direction).
Adiabatic (Gr. halOs passable) is when no heat flow takes place
during a change in state. As opposed to adiabatic boundary, the
diathermic boundary permits energy transfer as heat. Dialysis is
used to study the binding of small molecules to macromolecules.
It is very slow and is accelerated by applying electricity, when it
is called electrodialysis.
4.14 Shapes ofMolecules
4.14.1 General Shape: Morphe is shape in Greek, giving rise to
terms, e.g., amorphous, isomorphic, idiomorphic (Gr. idios own,
distinct) and polymorphic shapes taken by solid substances.
Albtriomorphic (Gr. allotrio alien) means non-crystalline in
outward form (but crystalline in internal structure). In a
mesomorphic (Gr. mesos middle) substance, atoms/molecules are
oriented in parallel planes of a layered structure. Such substances,
e.g., a detergent, are associated with smectic phase (L. smectus
cleansing; Gr. soapy).
The orderly close packed hexagonal arrangement of micelles in
concentrated surfactant solutions as arrays of long cylinders is
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Trigonal
(bipyramidal) ,
hexagonal and
octagonal shapes
of crystal geometry
are common.
called a lyotropic mesomorph (mesos middle). A morphotropic
transition is an abrupt change in the structure of a solid solution
that occurs when the composition is gradually varied. A
monotropic transition refers to a single morphotype that occurs
in the irreversible transition from a metastable polymorphic
form to the stable polymorph, e.g., transition of aragonite to
calcite (CaC0 3). In polymorhic transition, a reversible transition
occurs at a certain temperature and pressure (the inversion
point) of a solid crystalline phase to another phase of the same
chemical composition but with a different crystal structure.
Polymorphic transition is synonymous with enantiotropic
transition.
4.14.2 Angles and Faces: The torsion angle (also called dihedral
angle) between bonds of two groups (A and D in the A-B-C-D
system) can be variable. Its designation is done depending on
the range to which the torsion angle belongs - synperiplanar (sp,
0° to 30°), synclinal (sc, 300 to 90° and -30° to 90°), anticlinal (ac,
90° to 150° and -90° to -150°) and antiperiplanar (ap, ± 150° to
180°).
Gonia is angle, and hedra is seat (facelbase) in Latin. Agonist and
antagonist are angle-related terms. [3] Trigonal (bipyramidal),
hexagonal and octagonal shapes of crystal geometry are common.
A delta (~) hedron is a polygon with all faces that are equilateral
(later side) triangles. The common morphologies of crystals are
tetrahedral (n=4) and octahedral (6), and trigonal bipyramid (5).
A few eicosahedral (20 faces, n= 12) molecules are known. They
include some of the boranes and buckminsterfullerene. The
latter name is from Buckminster Fuller, an American architect
known for his designs of hemispherical domes consisting of
pentagonal and hexagonal faces. Enneahedron (ennea nine) is a
solid figure with nine faces.
The organometallic cage compounds are of different geometries
depending on the number of framework electrons involved closo (2n+2), nido (2n+4), arachno (2n+6) or hypho (2n+8). In
Greek, closo means closed, arachno means spider's web and hypho
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means net. In Latin, nido means nest, giving an indication of the
morphology of the structures.
Trope of entropy is
intended to mean
that useful energy
4.15 Work is Done Anyway
'Ergon', in Greek is work. In an exergonic (exo outside) reaction
(LlG<O), energy is released that may be transferred as work or
heat. If the transferred energy is in the form of heat, it is
exothermic. In an endergonic (endo within) reaction (LlG>O),
work is done on the system. If it is the heat that is consumed
(from the surroundings), it is endothermic.
is turned to less
useful energy.
4.16 Enabling
The prefix 'en' is an enabling prefix used for words of Latin/
French origin in the sense of in/into/upon or words of Greek
origin in the sense of in. Enthalpy (Gr. enthalpein to warm in),
entropy (Gr. tTOpOS a turning, see above). Enthalpy is a
thermodynamic property or state function. Trope of entropy is
intended to mean that useful energy is turned to less useful
energy. Thus, entropy is a measure of the energy that is
unavailable for doing work since it exists as the internal motion
of molecules. It is thus a measure of the disorder of a system.
4.17 It's about Fleeing Away
The term 'centrifugal' (L.fugere flee) is associated with a tendency
to flee away from the centre (the opposite of centrifugal is
centripetal; L. petere to seek). Fugacity is the tendency of a gas to
expand or escape. Leaving groups are termed 'luges'; one that
carries away the bonding electron pair (e.g., Cl-in the hydrolysis
of RCl) is called a nucleofuge, and one (e.g., H+ in the nitration
of benzene) that carries away the positive charge is called an
electrofuge [3]. The reagents' OH- of the former reaction is a
nucleophile (Gr. philos friend), and the N0 2 + of the latter
reaction, an electrophile. The tendency to depart as the charged
species is termed as nucleofugality and electrofugality respectively [3].
The term 'centrifugal'
(L. fugere flee) is
associated with a
tendency to flee away
from the centre (the
opposite of centrifugal
is centripetal; L.
petere to seek).
Fugacity is the
tendency of a gas to
expand or escape.
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In polymer
nomenclature,
atactic, syndiotactic,
etc. indicate the
tacticity. In epitaxy, a
unified crystal growth
or deposition of one
crystal layer on
another is effected.
4.18 Cloud Physics at Work
Talking of cloud to a chemist instantly brings the classical
Wilson's cloud chamber, a simply named term to his attention.
Cloud is Nephele in Greek; nephelometry is the measurement of
concentration by the principle of scattering of light by the
colloidal suspensions. Nephelauxetic effect (Gr. auxein to increase,
cf., auxins, auxochrome etc.) is in particular reference to electron
cloud.
4.19 Roots o/Common Biological Terms in Chemistry
Theexo-endo pair of prefixes (Section 4.15) is used extensively in
biology. Endocytosis (Gr. kytos vessel, case) is the uptake by a
cell of particles that are too large to diffuse through the cell wall.
It includes both phagocytosis (phagos mouth; phag to eat) and
pinocytosis. Exocytosis is the discharge from a cell of particles
too large to diffuse through the cell wall.
'Taxis' (Gr. arrangement) is the noun form of tactic (Gr. taktos
order), e.g., phototaxis, chemotaxis, etc. Phototaxis is moving
towards light. The opposite phenomenon of moving away from
light is by negative phototactic response. In polymer
nomenclature, atactic, syndiotactic, etc. indicate the tacticity. In
epitaxy, a unified crystal growth or deposition of one crystal
layer on another is effected.
Cytoplasm (Gr. plassein to mould, plastos moulded, c.f., plasma,
chloroplast) is the protoplasm of a cell, apart from that of the
nucleus. Erythrocytes (Gr. erythros red) are red blood corpuscles,
leucocytes (Gr.leukos white) are white corpuscles of the blood or
lymph. 'Gen' (Gr. gennaine to generate) occurs as suffix in
androgen (Gr. andros man), and estrogen (oistros frenzy). The
latter is a female steroid sex hormone that maintains the menstrual
cycle; it was so named probably to imply that the women were
off-balance during their periods. 'Moneres' in Greek is single. A
hormone (Gr. horme impulse) is an internal secretion which on
reaching some part of a plant/animal body exercises a physiological
action, while pheromone (Gr. pherein to bear) is a chemical
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CLASSROOM
substance secreted by an animal which influences the behaviour
of others of its species, e.g., queen bee substance. It can be
termed as an ectohormone. In chemical ecology (Gr. oikos house,
logos discourse), allomone (Gr. alios other) has a similar genealogy.
The term valency
is from va/ere
(Latin) that means
'to be strong'.
'Soma' in Greek is body, e.g., chromsome (Gr. chroma colour).
'Trophe' (Gr. trophos food) is nourishment, e.g., autotroph,
auxotroph, heterotroph, mesotroph (mesos middle), polytroph,
oligotrophic (oligos few) and eutrophic (eu well). 'Voro' in Latin
is to devour, e.g., herbivore, insectivore, omnivore (L. omnis all).
An enzyme (Gr. zyme leaven; zymos fermentation) is a substance
that helps fermentation. A zymogen is a proenzyme. Isozymes
are electrophoretically distinct forms of an enzyme with identical
function.
4.20 Some Left-outs
Gravis is heavy in Latin, as in specific gravity and gravimetric
(metron measurement). Gyrus, also of Latin is a circle, e.g.,
'magnetogyric ratio' which is the ratio of magnetic moment to
angular (gyric) moment. The term valency is from valere (Latin)
that means 'to be strong'. Stoichiometry (Gr. stoicheion an
element) is the determination of exact proportion of elements to
make pure compounds, complexes, etc. The word 'canon' (Gr.
kanon a straight rod), in music, is to piece with different parts.
taking up the same theme successively. Canonical rate constant
is the rate constant of a system in which the reacrtants are in
thermal equilibrium at a given temperature. Canonical structures
are rod-like.
Vulcanus in Latin is the God of fire. Vulcanisation is the heattreatment of rubber with sulphur to increase the strength.
'Galvanic' is from Luigi Galvani, the discoverer of galvanic
action. Zeolites are any of a large group of aluminosilicates of
N a, K, Ca, and Ba, containing very loosely held water. The word
is derived from the Greek root zeiin which means 'to boil' and
lithos, 'a stone', and is an allusion to the fact that many zeolites
intumesce (i.e., swell up) under the blow pipe. A zwitter ion
(Ger. zwitter a hybrid) is an ion carrying both a positive and a
Vulcanus in Latin
is the God of fire.
Vulcanisation is
the heat-treatment
of rubber with
SUlphur to increase
the strength.
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The knowledge of
the etymology of
chemistry terms
can potentially
remove their often
intimidating
appearance and
help understand
the concepts
represented by
them succinctly.
negative charge, e.g., amino acid. Viscose (L. viscosus sticky) is
the viscous sodium salt of cellulose xanthate.
5. Conclusion
Historically, most chemistry terms are derived from Classical
Greek and Latin word roots. The trend still continues as newer
concepts are being developed and given names. There are about
a dozen most frequently used affixes - ortho, tropo, mer, meta, iso,
para, hetero, syn, homo, topo, dia and pseudo. For a starter, the
knowledge of the etymology of chemistry terms can potentially
remove their often intimidating appearance and help understand
the concepts represented by them succinctly. And this can be a
basis for further development. As one progresses, it may appear
in few cases that due to the advancement in science the original
concepts got refined though, they still retain the original terms
coined for them, and that the etymology approach may be
misleading. Not taking the etymology approach so far that it is
an added burden; on the other hand, a means to take positively
on the heavily loaded chemistry curriculum is expected to be one
step in replacing sobriety with a pleasurable learning experience.
Suggested Reading
[1] Chambers Dictionary ofScience and Technology, Allied Publishers: New
Delhi, 1986.
[2] Chambers English Dictionary, Allied Publishers: Ahmedabad, 1989.
[3] A D McNaught and A Wilkinson, Compendium of Chemical Terminology, The Gold Book, 2nd ed, IUPAC & Blackwell Science, 1997.
[4] I L Finar, Organic Chemistry, Vols. 1 and 2, 5th ed., Pearson Education:
England, 2000.
[5] J March, Advanced Organic Chemistry - Reactions, Mechanisms and
Structure, 4th ed.; John Wiley & Sons (Asia), Singapore, 2001.
[6] P AtkinsandJ de Paula, Physical Chemistry, 7thed,Oxford Univ. Press.,
Oxford, 2002.
[7] J E Huheey, E A Keiter and R L Keiter, Inorganic Chemistry, Principles
ofStructure and Reactivity, 4th ed, Pearson Education Inc., New Delhi,
2000.
[8] N S Sarma, J. Chem. Edu., Madison, USA, Vol.Sl, pp.1437-1439, 2004.
[9] G J Leigh, H A Favre and W V Metanomski, Principles of Chemical
Nomenclature, A Guide to IUPAC Recommendations, Blackwell Science, 1998.
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